Electronic devices face continued pressure to design and produce their configurations in a further state of miniaturization, ergonomically pleasing shapes, and a reduced weight. To achieve these goals, many choices in materials of construction and shape must be exercised during upstream manufacturing. Whenever changes occur in the product, invariably there are also changes in tooling. Retooling a fabrication facility requires significant time and cost for requalification. For electronic manufacturing, the substrate must be held uniformly in place during several process steps, including lithography and deposition. Thin solid materials are typically held in place by affixing to a rigid carrier. Carrier substrates may be composed of sapphire, quartz, certain glasses, or silicon, exist in thicknesses from 0.5-1.5 mm (500-1,500 um), and be of larger area than the work unit. Challenges exist in choosing a means of adhesion that offers sufficient adhesive force and quality to withstand the manufacturing process that may include aggressive grinding, polishing, or other mechanical practices, while allowing work units of varying size and shape to be easily removed without damaging their integrity.
Several work unit sizes and shapes are being considered for use in manufacturing. Semiconductor wafers may range in diameters from less than two inches (2″=50 mm) to twelve inches (12″=300 mm), with 12″ being the current size used in most high volume manufacturing processes. Within this electronics sector, research is underway with next generation substrates at eighteen inches in diameter (18″=450 mm). Desired thickness of these substrates vary, but most intend to achieve 0.1 mm (100 um) with many in high volume manufacturing to below 0.05 mm (50 um). Handling semiconductor substrates down to these thicknesses is a significant challenge for a manufacturing process which uses conventional tooling.
In the display market, conventional glass substrates are being reduced in thickness to 0.1 mm (100 um) or less. In some cases, alternatives to glass are being considered, including non-glass inorganic and organic materials that exhibit intrinsic properties to support the application of layered metal and dielectric patterns onto its surface to a sufficient level necessary to produce an electronic device. In some cases, the work unit not only supports the laminated electronic layers but also offers sufficient tensile strength and ductility and/or elasticity to allow bending of the substrate in configurations necessary to classify it as a flexible display. These work units may vary in thickness to as high as 100 um or to below 10 um. Whether the material is glass or ceramic, metal, organic, or a composite, they require certain care in the handling, affixing, and removal from carrier substrates. It is well known that as material type, thickness, and shape varies, the method and means to handle such units will also vary. For example, the handling of a 12″ diameter round piece of domestic type aluminum metal foil (e.g. thickness 2 mil, ˜50 um), although it will wrinkle, is easier to handle than the same size and thickness of silicon, which is prone to cracking and breaking and is unable to support its own weight. As the need for adjusting the tooling and support required to handle work units of various shapes, sizes, and thicknesses, so also exists the demand for adhesives that can be tuned to the needs of the process.
Common tape adhesives do not adequately support work units with the necessary rigidity and uniformity to meet electronic processing objectives and thin substrates to below 0.05 mm. The tape adhesive is much too elastic for mechanical stability during certain manufacturing steps such as polishing or grinding. Additionally, the composition of many tapes are based upon acrylic or silicone chemistry and are observed to exhibit outgassing (weight loss) due to material degradation at elevated temperatures at or above 250 C. The characteristic of outgassing will cause gas bubbles in-between the work unit and carrier substrate which in the case of very thin conditions, may cause deformation to the surface of the thinned work unit, and in severe instances, will perforate the surface to cause catastrophic damage to sensitive circuitry deposited upon the surface. For both mechanical and thermal resistance, there is a need for a system that can be inserted between two hard substrates and achieve the necessary thermal and chemical resistance requirements of the customer process. In this case, a thermal resistance that reaches 250 C or more is necessary. To this end, it is desired to have a porous adhesive which offers sufficient thermal and chemical resistance to support electronic manufacturing processes for semiconductor and display operations and is easy to remove by allowing liquid penetration by capillary action, effect on reducing adhesion of the work unit and carrier substrate, and their subsequent release and separation without harm to the work unit.